The overall objective of the research grant is to diagnose pulmonary edema by a microinvasive technique which measures the density change of blood. The specific aims of the research plan are 1) to develop a density comparator to measure the density difference between the arterial and venous blood of the lung for quantifying pulmonary fluid filtration and 2) to use the density meter to monitor the response of the lung to hypertonic disturbances. The basic principle of the comparator is the employment of a set of mechanical U-tubes with blood flowing through. The density of the blood is determined by the change in the resonant frequency of the U-tube oscillator. It is found that the density change of venous blood is quite significant when hypertonic disturbance is imposed onto the pulmonary circulation. A theoretical stimulation suggests that the procedure can be used to determine the filtration characteristics of pulmonary endothelium and the compliance of the interstitial tissue. Both values are useful to characterize the development of pulmonary edema.